The invention relates to a rotary piston engine in trochoidal design with a rotor housing, made of light metal, and with side parts, which are made of light metal and in which bearing bodies are installed to receive an eccentric shaft.
Many variants of mass-produced rotary piston engines exist, an example of which is given in DE 40 03 663 C. Usually they comprise side parts made of gray cast iron and held together with the trochoidally shaped rotor housing by means of axial tie rods. All forces between the side parts and the rotor housing are transferred between the adjoining surfaces by means of friction lock. This friction lock is produced by pre-stressing the axial tie rods. The bearing bodies for the bearings of the eccentric shaft are designed usually like a flange and are fastened to the side parts by means of axially oriented screws.
To achieve an optimal weight to power ratio for the engine and to provide additionally for good heat dissipation at high power output, the side parts can be made of light metal, in particular of an aluminum alloy. In known engines of this design and in particular in engines with supercharge operating mode and charge stratification, the mechanical problems are greater. After a relatively short operating time, the side parts crack. In addition, the rotor housing shifted radially in relation to the side parts. The application of higher axial pre-stresses does not lead to satisfactory results, because with the use of aluminum components the results are inadmissibly high material stresses and thus additional problems. Even the use of greater material thicknesses does not lead to satisfactory results, because the dissipation of heat becomes worse and the weight is increased.
The invention is concerned with the problem of designing a light metal rotary piston engine of the type described in the introductory part in such a manner that a high structural strength and thus high operational safety are achieved.
This problem is solved in that the bearing bodies are held in an area, in which the maximum gas pressures develop, by at least one tie rod. The tie rod is oriented approximately radially to the bearing body and is connected to a support element, which rests externally on the side parts and the rotor housing.
The use of tie rods results in high structural strength at relatively low weight increase. In addition, a connection, which is shape locking in the radial direction, is produced between the rotor housing and the side parts, where the housing forces and the bearing forces are transferred substantially to the tie rods. The axial screw couplings must be pre-stressed only to the extent that the sealing function is reliably fulfilled.
In an exemplary design of the invention, two tie rods are provided for each bearing body, of which one is disposed approximately in the plane of symmetry of the rotor housing and the other, at an angle ranging from approximately 30 degrees to approximately 45 degrees in the rotational direction of the plane of symmetry. Thus the area of maximum gas pressures is reinforced in an adequate manner.
In an advantageous design of the invention tension bolts, extending through the side parts, are provided as the tie rods. To this end high strength steel screws can be used. The bearing bodies and the support elements are made of gray cast iron or steel so that they exhibit a significantly higher structural strength than aluminum.
Another design of the invention provides that the bearing bodies exhibit a partially cylindrical outer surface and are held on the counter-surfaces of the side parts by the tie rods. The result is ample clearance for the bearing and rotor cooling oil to drain inside the side parts.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.